def isprime(a):

    for b in range(2,int(a**(1/2))+1):

        if a%b==0:

            return False

    return True

digits ={

    "zero":0,

    "one":1,

    "two":2,

    "three":3,

    "four":4,

    "five":5,

    "six":6,

    "seven":7,

    "eight":8,

    "nine":9,

}

n=input().split(" ")

r = ""

j=0

k=0

for i in n:

    if i in digits:

        r=r+str(digits[i])

    else:

        print("nepravilno bot!")

        exit()

r = int(r)

for l in range(r, r*1000):

    if isprime(l):

        j=l

        break

for z in range(r,2,-1):

    if isprime(z):

        k=z

        break

if r-k>j-r:

    print(j)

else:

    print(k)